1. Field of the Invention
This invention relates to a friction clutch.
2. Background Information
On some motor vehicle friction clutches as shown in FIG. 2 in German Patent No. 42 39 289 A1 (not prior art), the pressure plate is fastened to a flywheel with the interposition of a clutch disc with friction linings and lining springs, whereby the pressure plate and the flywheel have a common axis of rotation. The pressure plate is provided with an application plate located non-rotationally--but so that it can move axially--in a clutch housing, and is provided with a membrane spring which acts as an application means, whereby the membrane spring is connected to studs or pins fastened to the clutch housing. To release the clutch, a release mechanism is placed in contact with the radially inner ends of flexible tabs of the membrane spring, on its side facing away from the application plate. When the release mechanism is displaced from its initial position toward the application plate, the flexible tabs of the membrane spring are deformed so that their ends are moved radially outside the studs of the application plate, whereby first the application force exerted by the application plate on the friction lining of the clutch disc is reduced to zero, and then the application plate, assisted by the action of leaf springs located in the circumferential area and connecting the application plate to the clutch housing, is pushed away from the clutch disc. Conversely, to engage the clutch, the membrane springs are relaxed and displaced by the release mechanism, while it, the membrane spring, is relaxed, first to apply the application plate against the friction lining of the clutch disc, and then, upon further relaxation, to apply the application force. Since the membrane spring experiences a deformation both during the application/removal of the application force and during the displacement of the application plate relative to the clutch disc, its deformation resistance must be overcome during the entire release and engagement process. The amount of work which must be performed is therefore relatively high.
During the clutch release and engagement process, along the entire deformation travel of the membrane spring, a translation or translation ratio is applied which is a function of the distance between the release mechanism and the studs in relation to the distance between the latter, the studs and the point of contact of the membrane spring with the application plate. On account of the length of the deformation travel of the membrane spring, the translation which can be achieved with such pressure plates is limited, generally to approximately 3:1, so that the amount of force which must be applied to the release mechanism, called the release force below, is relatively high. On a friction clutch of the prior art, therefore, it would be helpful if, during the release, the lining springs on the clutch disc would effect a gradual reduction of the transmissible torque by a reduction of the application force. By maintaining a constant position of the membrane spring in the clutch housing by means of an adjustment device, provisions would be made so that the application force, and thus by means of the above-mentioned translation, the release force does not increase further when the friction linings are worn.